1. Field of the Invention
The invention relates to a stud detectors.
2. Description of Prior Art
The invention relates more particularly to a stud detector that is capable of detecting wooden studs, metal objects or wires, and live wires carrying an AC current.
Stud detectors are well-known and rely on detecting changes in dielectric constants. The stud detectors are typically used by tradesmen to detect wooden studs or beams that are hidden from view, behind plaster or other wall coverings, by moving the detector across and closely adjacent a wall surface. It is necessary to determine the relative position of the studs so that other construction items or fittings can be securely attached the wall. For example when fitting a ceiling fan, support anchor bolts must, where appropriate, be screwed into ceiling joist that is above and behind the ceiling plaster. It is therefore desirable to locate the ceiling joist without damaging the ceiling coating. A portable stud locating device is fully described in U.S. Pat. No. 4,099,118.
The tradesman may also wish to locate any live electric wires that are likewise hidden from view behind a plastered or covered surface. A device that combines wooden stud detection and live wire location is described in U.S. Pat. No. 4,464,622. The combined device has improved calibration, but a disadvantage that the AC detection is dependent the wood detector circuit operation.
Further, the described combined device of U.S. Pat. No. 4,464,622 is incapable of detecting electric power cables that are disconnected from a mains supply or detecting metallic conduits, strips or other objects that may be important for the tradesman's activities. Such metallic elements may be required in some cases to provide a sound anchorage for a construction addition or wall fitting, for example. In other cases, the metallic elements may represent an impediment to anchorage of any fixings and so must avoided.